What are the parts of your knee joint?

You have four ligaments in your knee joint, and some of them can tear very easily. You can tell if you tore a ligament in your knee based on your symptoms and X-ray, MRI, and arthroscopy tests.
You have four ligaments in your knee joint, and some of them can tear very easily. You can tell if you tore a ligament in your knee based on your symptoms and X-ray, MRI, and arthroscopy tests.

You have four ligaments in your knee joint, and some of them can tear very easily. The problem is that a torn knee ligament has similar symptoms to other common knee injuries

This means that you shouldn’t automatically assume that you’ve injured a ligament if you’re having problems with your knee. Instead, you should seek immediate medical attention for an accurate diagnosis. It can also help if you take the time to learn the parts of your knee and what the most common knee injuries are. 

Your knee joint is a complicated hinge structure. It needs to bend and move flexibly so you can walk and perform daily tasks. 

Your knee joint is composed of many different parts including: 

  • Bones. Your thigh bone and shin bone come together at your knee joint. They’re protected and supported by your knee cap. 
  • Articular cartilage. This slippery tissue cushions your bones and allows them to glide past one another as you move.
  • MeniscusYou have two wedge-shaped pieces of cartilage in this joint that act as shock absorbers. It’s the type of cartilage most commonly damaged within this joint. 
  • Tendons. These connect your muscles to your bones. There are two main tendons in your knee joint. 

There are also four ligaments in your knee joint. Ligaments are tough, flexible tissues that connect your bones to other bones and help stabilize joints. The ones in your knee are the: 

  • Anterior cruciate ligament (ACL). This is front and center in your knee and connects your thigh bone to your shin bone. It helps with rotational movements and the forward motion of your shin bone. 
  • Posterior cruciate ligament (PCL). This is located in the back center of your knee. It also connects your thigh bone to your shinbone and controls the backward movements of your shin. 
  • Lateral collateral ligament (LCL). This ligament is on the outer side of your knee and connects your thigh bone to a small lower leg bone called the fibula. 
  • Medial collateral ligament (MCL). This stabilizes the inner side of your knee and connects your thigh bone to your shin bone.

What are the most common knee injuries? 

Your ligaments are the most frequently injured part of your knee. Some ligaments are injured more frequently than others. There are also several other injuries that can occur within this joint. Often, many of these injuries happen simultaneously as the result of a particular event, like a car crash or sports-related accident. 

Some of the most common knee injuries include: 

  • Damage to your ACL
  • Damage to your PCL
  • Tears in your meniscus
  • Tears in one or many of your tendons
  • Broken bones
  • Dislocations — when the bones in a joint are out of alignment

How can you injure a knee ligament? 

There are many different ways to injure the ligaments in your knee, from a single misstep to a powerful impact. Certain motions can injure each ligament. 

Your ACL is the most commonly injured ligament. This ligament is also the most likely to completely tear into two distinct pieces. You can tear your ACL in a single move by twisting your knee while your foot remains planted on the ground. 

Your PCL is the second most injured ligament in the knee. This ligament is far less likely to tear from a single misstep. Instead, it’s most often broken from a hard, sudden impact to the front of your knee. This could be from a car accident or when you’re tackled while playing football. 

Your MCL tears more often than your LCL, but they are vulnerable to the same events. Both types of tendon injuries are caused by a blow to the side of your knee. This can easily happen while playing sports. 

Other ways to injure a ligament and other parts of your knee joint include: 

  • Overextending your knee
  • Stopping suddenly when running
  • Landing on a flexed knee
  • Suddenly shifting your weight from one leg to the other

How is a torn ligament diagnosed? 

Your doctor will need to evaluate your knee in person to diagnose the underlying injury. They’ll likely use several imaging tests to determine the total amount of damage within your joint. 

Imaging methods can include: 

  • X-rays. These help view the bones in your joint. They can tell if a bone is broken and other possible tissue injuries. 
  • MRI. This is an excellent way to visualize soft tissues, like ligaments. It allows your doctor to look for tears in tissues that surround the bones in your joint. 
  • Arthroscopy. This is a minimally invasive way to look inside your knee joint. A camera mounted on a thin tube is inserted into your knee through a small incision. This is a helpful method for evaluating degenerative conditions within the joint and other details of internal injuries.  


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What are the symptoms of an injured knee ligament?

You may know right away that you’ve injured your knee. Some of the symptoms of a torn ligament appear instantly. The rapid onset of symptoms is one way to distinguish a torn ligament from other common knee injuries. For example, you might hear a popping sound when a ligament tears. 

Other symptoms include: 

  • Pain — although some cruciate ligament tears don’t involve pain, ligament pain can also be sudden and severe
  • Swelling — within 24hours after the injury
  • Trouble putting weight on your knee — or pain when you do
  • A loose or unstable feeling within the joint
  • Loss of your full range of motion

What is the treatment for an injured knee ligament?  

The treatment for your knee injury will depend on severity. Ligament injuries can range from slight overextensions to complete tears. Milder injuries will heal on their own with proper attention. 

Treatments for mild to moderate injuries include: 

  • RICE. Keep your leg well-rested, on ice, compressed with a wrap or bandage, and elevated for the fastest healing time.  
  • Immobilization. Your doctor could recommend a knee brace to help support the joint.
  • Physical therapy. More severe injuries could require physical therapy to strengthen your body and provide long-term support to your joint. 
  • Nonsteroidal anti-inflammatory drugs (NSAIDs). These can help with pain and inflammation in the joint while you heal. Ibuprofen is a common example. 

More severe injuries, like complete ACL tears, will need surgery before healing properly. Your doctor will determine whether or not you need surgery on a case by case basis. 

You should get medical help as soon as you realize that you’ve injured your knee. This is the best way to determine the underlying problem and efficiently treat it. 

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Medically Reviewed on 5/23/2022

Johns Hopkins Medicine: "Ligament Injuries to the Knee."

Maine Health: "Knee Ligament Injury."

OrthoInfo: "Anterior Cruciate Ligament (ACL) Injuries," "Common Knee Injuries," "Posterior Cruciate Ligament (PCL) Injuries."